The invention relates to an optical sensor.
Optical sensors of this type are generally used for detecting objects within a monitored area. In particular, these optical sensors are used for the technical equipment employed in security systems for which the area monitored with the optical sensor represents a danger zone of the system, for example a machine, a working tool, a robot or the like.
Optical sensors used for such monitoring tasks in particular can be embodied as area distance sensor. An area distance sensor of this type is known, for example, from the German patent document DE 103 26 848 A1. The sensor described in this document is used for detecting objects in a monitored area and is provided with a transmitter for emitting light rays, a receiver with thereto assigned receiving optics for receiving light rays which has a specified field of view that is admitted by the receiving light rays, and a deflection unit for the periodic deflection of the transmitted light rays within a specified angular range that defines the monitored area. An object-detection signal is generated at the receiver output of an evaluation unit, in dependence on the receiving signals. A short-range optics is arranged in the field of view for the receiving optics, wherein the segment of the field of view of the receiving optics which is covered by the short-range optics can be adjusted with the aid of an adjustment unit.
Sensors of this type are generally configured such that the transmitter and the receiver are installed immovably at a location, meaning they are arranged stationary. For conducting the transmitted light rays within a flat area to be monitored, the deflection unit is the only rotating and thus movable part of the optical sensors which are integrated into a housing. The deflection unit typically consists of at least one motor-driven mirror for deflecting the transmitted light rays and preferably also the received light rays.
However, one disadvantage of area distance sensors of this type is that they require a large amount of space for the deflection unit, so that the area distance sensor on the whole has an undesirably large structural form.
A further disadvantage is the extremely long path traveled by the transmitted light rays that extends from the transmitter via the deflection unit to a window in the housing through which the transmitted light rays leave the optical sensor. The same is true for the receiving light rays which enter the housing via the window in the housing and are deflected via the deflection unit to the receiver, thereby resulting in internal reflections of the transmitted light rays and the receiving light rays within the housing, which consequently reduce the detection sensitivity of the optical sensor.
A further disadvantage is that the deflection unit, which deflects the transmitted light rays and the receiving light rays, is normally tilted relative to the beam axes for the transmitted light rays and the receiving light rays, so that the cross sections of the transmitted light rays and the receiving light rays are deformed during the reflection at the deflection unit. This change in the beam cross section also causes a reduction in the detection sensitivity of the optical sensor.